1. Field of the Invention
This invention relates to a high-speed yarn feeding apparatus for transferring a synthetic yarn supplied continuously from a yarn supply source to a yarn pickup apparatus.
2. Description of Prior Art
Generally, a synthetic yarn is produced by extruding a polymer such as polyamide and polyester in a molten state from a spinning apparatus to form continuous filaments. The filaments are then cooled and passed through a feeding apparatus to a takeup apparatus which winds the filaments. The feeding apparatus usually comprises at least one positively rotating roller (usually called a godet roller) which contacts and advances the filaments.
An air ejector (usually called a suction nozzle or gun in a factory) is generally employed for threading the yarn filaments from the spinning apparatus through the feeding apparatus to the takeup apparatus. The travelling yarn supplied continuously from the spinning apparatus is sucked and drawn off by the suction nozzle. The yarn is then threaded from the spinning apparatus to the takeup apparatus by a person moving the suction nozzle along a thread line through the feeding apparatus. The feeding apparatus generally consists of one or more positively rotating rollers and several yarn guides positioned in appropriate places. The takeup apparatus typically includes a rotatable tube or bobbin on a winder.
In recent years, the winding speed of the winder has been increased and is typically operated at a speed of about 6,000 meters per minute (m/min) or more. Such a process is disclosed, for example, in U.S. Pat. No. 4,134,882. The increased winding speed of the winder is also reflected by the positive rotating rollers along the thread line. This increased speed causes a particularly difficult problem during the threading operation of the yarn from the spinning apparatus to the takeup apparatus.
If the suction force on the suction nozzle is that which is typical of air ejectors generally employed, the yarn cannot be drawn from the positively rotating roller after the yarn has been introduced to the roller. It is believed that this is principally due to the adhesion of the yarn to the surface of the roller and/or to the accompanying air stream generated around the roller by its rotation. This causes a yarn rolling-in or wrap-up on the roller which in turn prevents any further threading of the yarn. The difficulty in the threading operation becomes greater as the yarn transfer speed on the positively rotating roller becomes higher and the volume of the yarn becomes greater hence requiring an even greater suction to draw off the yarn from the roller.
Employing even the best commercially available suction nozzles under optimum conditions permits the threading of yarn having a travelling speed of at most about 3,500 to 4,000 m/min.
In Japanese Patent Publication No. 49778/72, a very high performance suction nozzle has been proposed which requires the use of a pressure chamber of very large capacity and compressed air of a very high pressure in order to maintain the high suction force. In use, however, this high performance suction nozzle has the following problems: (A) worsening of the work environment due to extremely loud noise generation upon release of the compressed air; (B) consumption of the compressed air at a great rate making continuous yarn threading operation uneconomical; (C) even the slightest drop in the suction force leads to a failure in the yarn threading operation; and (D) in the event of such failure, one must wait until the pressure recovers in the pressure chamber before again attempting the yarn threading operation. During this wait, waste yarn is generated in great quantities.
Japanese Patent laid-open Number 8111/77 discloses a method of winding high speed spun yarn which includes a stepped roller as a yarn feeding apparatus. The yarn passes through a small diameter portion of the stepped roller at the time of the yarn threading operation so that the tension of the travelling yarn between the positively rotating roller and the winder is maintained higher than the tension at the time of normal winding, thus increasing the success rate for threading the yarn to the winder. After threading the yarn to the winder, the travelling yarn is moved from the small diametered portion to the large diametered portion of the roller by a yarn shifting guide. This method was developed with the object of increasing the efficiency and success of threading to a winder. The disclosed stepped roller has only a small difference in diameter between the large diametered portion and the small diametered portion. If the difference in diameter is increased, the travelling yarn cannot be moved from the small diametered portion to the large diametered portion by the yarn shifting guide because of the large gap in height between the surfaces of the two portions of the stepped roller.